scholarly journals Projections of historical and 21st century fluvial sediment delivery to the Ganges-Brahmaputra-Meghna, Mahanadi, and Volta deltas

2018 ◽  
Vol 642 ◽  
pp. 105-116 ◽  
Author(s):  
Frances E. Dunn ◽  
Robert J. Nicholls ◽  
Stephen E. Darby ◽  
Sagy Cohen ◽  
Christiane Zarfl ◽  
...  
Keyword(s):  
21St Century ◽  
Sediment Delivery ◽  
Fluvial Sediment ◽  
The Ganges

The physical sustainability of the coastal zone of the Ganges-Brahmaputra-Meghna delta under climatic and anthropogenic stresses

2021 ◽  
Author(s):  
Stephen Darby ◽  
Md. Munsur Rahman ◽  
Anisul Haque ◽  
Robert Nicholls ◽  
Frances Dunn
Keyword(s):  
Sea Level Rise ◽  
Sea Level ◽  
Average Rate ◽  
River Management ◽  
Tidal River ◽  
Natural Conditions ◽  
Fluvial Sediment ◽  
Average Value ◽  
Delta Plain ◽  
The Ganges

<p>The Ganges-Brahmaputra-Meghna (GBM) delta is one of the world’s largest deltas, and consists of large areas of low flat lands formed by the deposition of sediment from the GBM rivers. However, recent estimates have projected between 200~1000 mm of climate-driven sea-level rise by the end of the 21st century, at an average rate of ~6 mm/yr. Eustatic sea-level rise is further compounded by  subsidence of the delta, which in the coastal fringes varies from 0.2 to 7.5 mm/yr, at an average value of ~2.0 mm/yr. Therefore, the combined effect of sea-level rise and subsidence (termed relative sea-level rise, RSLR) is around 8.0 mm/yr. Such high values of RSLR raise the question of whether sediment deposition on the surface of the delta is sufficient to maintain the delta surface above sea level. Moreover, as the total fluvial sediment influx to the GBM delta system is known to be decreasing, the retained portion of fluvial sediment on the delta surface is also likely decreasing, reducing the potential to offset RSLR. Within this context, the potential of various interventions geared at promoting greater retention of sediment on the delta surface is explored using numerical experiments under different flow-sediment regime and anthropogenic interventions.  We find that for the existing, highly managed, conditions, the retained portion of fluvial sediment on the delta surface varies between 22% and 50% during average (when about 20% of the total floodplain in the country is inundated) and extreme (> 60% of the total floodplain in the country is inundated) flood years, respectively. However, the degree to which sediment has the potential to be deposited on the delta surface increases by up to 10% when existing anthropogenic interventions such as polders that act as barriers to delta-plain sedimentation are removed. While dismantling existing interventions is not a politically realistic proposition, more quasi-natural conditions can be reestablished through local- sediment management using tidal river management, cross dams, dredging, bandal-like structures and/or combinations of the above measures.</p>

Dynamics of sediment delivery to mangrove forests of the Ganges-Brahmaputra-Meghna Delta

2020 ◽  
Author(s):  
Richard Hale ◽  
Alexandra Garnand ◽  
Carol Wilson
Keyword(s):  
Sediment Load ◽  
Monsoon Season ◽  
Sediment Concentration ◽  
Water Velocity ◽  
Sediment Supply ◽  
Tidal Range ◽  
Mangrove Forests ◽  
Southern Coast ◽  
Sediment Delivery ◽  
The Ganges

<p>The Ganges-Brahmaputra-Meghna Delta (GBMD) is among the largest in the world, nourished by the ~1 Gt/yr sediment load of its titular rivers. Approximately 75% of this sediment load is debouched to the Bay of Bengal, with ~180 Mt subsequently reworked by tidal processes across the southwestern portion of the delta. This region includes this Sundarbans National Reserve Forest (SNRF), which is the words’ largest continuous mangrove stand. In addition to global sea level rise and the enhanced subsidence intrinsic to deltas, ongoing and proposed alterations to the upstream fluvial sediment supply threaten the future viability of this important ecological and cultural resource.</p><p> </p><p>In this study, we use data collected in situ by acoustic and optical instrumentation to examine the physical processes controlling sedimentation in the mangrove forest along the southern coast during both the monsoon (October 2019) and dry seasons (March 2020).  These data are then compared with sedimentation rates measured using sediment elevation tables and marker horizons, as well as observations made 100 km further inland near the northern extent of the SNRF. At this inland site, sediment supply, inundation depth, and salinity have been identified as important factors controlling sediment deposition to the mangrove platform, which ranges from ~1 cm during the dry season (November – June), to > 2 cm during the monsoon (July-October). Data from the second location along the coast are vital for understanding the regional nature of the various threats to delta viability.</p><p> </p><p>Preliminary analysis of the 2019 monsoon season data from the southern coast reveals the relative importance of water depth, water velocity, and mangrove pneumatophore density on modulating both water velocity and suspended sediment concentration. Previous studies have identified that while the inland location features a larger tidal range (~5 m vs. ~3 m), frequent cyclone activity likely impacts sedimentation at the coastal site. Data collected in March 2020 will address how these variables impact controls on sedimentation both seasonally and regionally. Results from this study demonstrate the importance of providing regional context to sedimentation studies, as delta communities adapt to dynamic forcing conditions.   </p>

scholarly journals Modelling the increased frequency of extreme sea levels in the Ganges–Brahmaputra–Meghna delta due to sea level rise and other effects of climate change

2015 ◽  
Vol 17 (7) ◽  
pp. 1311-1322 ◽  
Author(s):  
S. Kay ◽  
J. Caesar ◽  
J. Wolf ◽  
L. Bricheno ◽  
R. J. Nicholls ◽  
...  
Keyword(s):  
Climate Change ◽  
Sea Level Rise ◽  
Sea Level ◽  
21St Century ◽  
Bay Of Bengal ◽  
Hydrodynamic Model ◽  
Sea Levels ◽  
Extreme Sea Levels ◽  
The Ganges

A hydrodynamic model of the Bay of Bengal has been used to explore increasing frequency of extreme sea levels in the Ganges–Brahmaputra–Meghna delta over the 21st century.

scholarly journals A first look at the influence of anthropogenic climate change on the future delivery of fluvial sediment to the Ganges–Brahmaputra–Meghna delta

2015 ◽  
Vol 17 (9) ◽  
pp. 1587-1600 ◽  
Author(s):  
Stephen E. Darby ◽  
Frances E. Dunn ◽  
Robert J. Nicholls ◽  
Munsur Rahman ◽  
Liam Riddy
Keyword(s):  
Climate Change ◽  
Sediment Transport ◽  
Water Balance ◽  
Transport Model ◽  
Future Climate ◽  
Anthropogenic Climate Change ◽  
Fluvial Sediment ◽  
Sediment Transport Model ◽  
Sediment Loads ◽  
The Ganges

We employ a climate-driven hydrological water balance and sediment transport model (HydroTrend) to simulate future climate-driven sediment loads flowing into the Ganges–Brahmaputra–Meghna (GBM) mega-delta.

Sediment retention in river deltas and feedbacks with delta morphology

2021 ◽  
Author(s):  
Jaap Nienhuis ◽  
Juan Paniagua-Arroyave ◽  
Frances Dunn ◽  
Sagy Cohen ◽  
Torbjorn Tornqvist
Keyword(s):  
River Mouth ◽  
Sediment Traps ◽  
Sediment Supply ◽  
Sediment Retention ◽  
Sediment Delivery ◽  
Cross Sectional ◽  
Fluvial Sediment ◽  
River Deltas ◽  
Sediment Loads ◽  
The Mean

<p>Fluvial sediments have collectively formed about 900,000 km<sup>2</sup> of deltaic land since Holocene sea-level rise slowed down. The rate at which deltas have retained fluvial sediment to build deltaic land, however, has varied greatly between different deltas. Here we quantify sediment retention in the delta topset and foreset for 3,556 deltas globally. We estimate retention from data on delta morphology and cross-sectional area, combined with WBMSed data on fluvial suspended sediment supply. Deltas, on average, retain 25±2% (standard error of the mean) of the fluvial sediment in their topset and 31±2% in their foreset. Because topset sediment retention reduces the sediment delivery to the river mouth, it sets up a feedback with processes that build delta morphology. Waves reduce topset sediment retention whereas tides increase it. Tide dominated deltas retain 61±24% on their topset, on average, compared to 21±3% and 24±2% for river- and wave-dominated deltas, respectively. Larger deltas trap more sediment, but not in comparison to their larger sediment loads, making them relatively inefficient sediment traps.</p>

scholarly journals Projections of declining fluvial sediment delivery to major deltas worldwide in response to climate change and anthropogenic stress

2019 ◽  
Vol 14 (8) ◽  
pp. 084034 ◽  
Author(s):  
Frances E Dunn ◽  
Stephen E Darby ◽  
Robert J Nicholls ◽  
Sagy Cohen ◽  
Christiane Zarfl ◽  
...  
Keyword(s):  
Climate Change ◽  
Anthropogenic Stress ◽  
Sediment Delivery ◽  
Fluvial Sediment

scholarly journals A Sustainable Future Supply of Fluvial Sediment for the Ganges-Brahmaputra Delta

2018 ◽  
pp. 277-291 ◽  
Author(s):  
Stephen E. Darby ◽  
Robert J. Nicholls ◽  
Md. Munsur Rahman ◽  
Sally Brown ◽  
Rezaul Karim
Keyword(s):  
Fluvial Sediment ◽  
Sustainable Future ◽  
Future Supply ◽  
The Ganges

scholarly journals Observations and scaling of tidal mass transport across the lower Ganges–Brahmaputra delta plain: implications for delta management and sustainability

2019 ◽  
Vol 7 (1) ◽  
pp. 231-245 ◽  
Author(s):  
Richard Hale ◽  
Rachel Bain ◽  
Steven Goodbred Jr. ◽  
Jim Best
Keyword(s):  
Sediment Transport ◽  
Suspended Sediment ◽  
Suspended Sediment Concentration ◽  
Water Discharge ◽  
Sediment Concentration ◽  
Natural System ◽  
Sediment Flux ◽  
Sediment Delivery ◽  
The Ganges ◽  
Tidal Processes

Abstract. The landscape of southwest Bangladesh, a region constructed primarily by fluvial processes associated with the Ganges River and Brahmaputra River, is now maintained almost exclusively by tidal processes as the fluvial system has migrated east and eliminated the most direct fluvial input. In natural areas such as the Sundarbans National Forest, year-round inundation during spring high tides delivers sufficient sediment that enables vertical accretion to keep pace with relative sea-level rise. However, recent human modification of the landscape in the form of embankment construction has terminated this pathway of sediment delivery for much of the region, resulting in a startling elevation imbalance, with inhabited areas often sitting >1 m below mean high water. Restoring this landscape, or preventing land loss in the natural system, requires an understanding of how rates of water and sediment flux vary across timescales ranging from hours to months. In this study, we combine time series observations of water level, salinity, and suspended sediment concentration with ship-based measurements of large tidal-channel hydrodynamics and sediment transport. To capture the greatest possible range of variability, cross-channel transects designed to encompass a 12.4 h tidal cycle were performed in both dry and wet seasons during spring and neap tides. Regional suspended sediment concentration begins to increase in August, coincident with a decrease in local salinity, indicating the arrival of the sediment-laden, freshwater plume of the combined Ganges–Brahmaputra–Meghna rivers. We observe profound seasonality in sediment transport, despite comparatively modest seasonal variability in the magnitude of water discharge. These observations emphasize the importance of seasonal sediment delivery from the main-stem rivers to this remote tidal region. On tidal timescales, spring tides transport an order of magnitude more sediment than neap tides in both the wet and dry seasons. In aggregate, sediment transport is flood oriented, likely as a result of tidal pumping. Finally, we note that rates of sediment and water discharge in the tidal channels are of the same scale as the annually averaged values for the Ganges and Brahmaputra rivers. These observations provide context for examining the relative importance of fluvial and tidal processes in what has been defined as a quintessentially tidally influenced delta in the classification scheme of Galloway (1975). These data also inform critical questions regarding the timing and magnitude of sediment delivery to the region, which are especially important in predicting and preparing for responses of the natural system to ongoing environmental change.

Sign in / Sign up

Export Citation Format

Share Document